Pseudacteon obtusitus, Plowes, Robert M., Folgarait, Patricia J. & Gilbert, Lawrence E., 2015

Plowes, Robert M., Folgarait, Patricia J. & Gilbert, Lawrence E., 2015, Pseudacteon notocaudatus and Pseudacteon obtusitus (Diptera: Phoridae), two new species of fire ant parasitoids from South America, Zootaxa 4032 (2), pp. 215-220 : 217-219

Pseudacteon obtusitus new species

Fig. 5

Pseudacteon obtusus, Orr et al. 1997

Pseudacteon obtusus, Morrison & Gilbert 1999

Pseudacteon obtusus (small form), Porter and Pesquero 2001 Pseudacteon obtusus (small form), Folgarait et al. 2005 Pseudacteon obtusus (small form), Kronforst et al. 2007 Pseudacteon nr. obtusus, Folgarait et al.2007a , b Pseudacteon “mini” obtusus, Feener et al. 2008 Pseudacteon nr. obtusus, Patrock et al. 2009

Diagnosis. Females: distinguished from the similar P. obtusus ( Fig. 6 ) by the smaller size of P. obtusitus . The width of the oviscape in P. obtusitus ranges from 0.17 to 0.2 mm (N=22) while P. obtusus oviscape width is from 0.25 to 0.31 mm (N=16). The flagellomere 1 of P. obtusitus is conical and tapering with a fringe of fine hairs and a short or absent arista, while P. obtusus has a broader flagellomere 1, terminating in a long or short arista. Males: unknown.

Female. Body length 0.86 mm (paratype range 0.72– 0.01 mm), thorax width 0.35 mm (paratype range 0.28 – 0.40 mm). Wing length 0.9 mm, width 0.42 mm. Body color dark orange brown, frons dark grey. Palpus pale yellow. Flagellomere 1 pale brown, flat, conical tapering toward arista, microscopically pubescent, fringe of fine hairs either side of tapered tip, overall 0.18 mm long, extending about ¾ of the eye width. Arista, fine, up to one quarter the length of flagellomere 1 (but absent in some specimens). Frons with 2-2-4-4 setae and 1 pair of supra-antennal setae. Scutellum with 2 pairs of setae, posterior pair over twice the length of fine anterior pair. Costa with 14 pairs of dark 0.035 mm setae. Halter pale yellow brown. Legs pale yellow brown.

Abdomen: Tergite 6 dark brown, 2 fine setae on each lateral margin. Sternite 6 with a pair of medial setae, and 2 – 3 fine short setae on each side toward lateral margin. Oviscape in dorsal view broad, with two side lobes alongside the median lobe. Each side lobe sclerotized, rounded tip, with a small hyaline "tail" extending from the distal inner edge toward the median lobe. Hyaline tails terminate with an outward twist. Median lobe may act as a guide for the retractable stylet which passes between the straight dorsal plate and the down-curved ventral plate. 4 fine setae along each joint line between side and median lobes. Overall oviscape length 0.24 mm. Width across widest part at lobe tips 0.18 mm (paratype range 0.17 to 0.2 mm).

Distribution. La Plata basin of Argentina and Paraguay to São Paulo and Mato Grosso states, Brazil ( Patrock et al. 2009).

Etymology. The species name implies “small obtusus ” by combining “ obtusus ” with the Latinized form of the colloquial Spanish diminutive “-ito”.

Holotype. ♀, ARGENTINA: SANTA FE: Romang, 29.512º S, 59.744º W, 6.ii.2009, E.G. LeBrun, over S. invicta nest, BFL- 110739 d ( MACN).

Paratypes. ARGENTINA: FORMOSA: Herradura, 26.518º S, 58.287º W, 1♀, 29.xi.2003, E.G. LeBrun, over S. invicta nest ( LACM); MENDOZA: La Consulta, 33.73º S, 69.12º W, 3♀, 22–26.i.2007, 5♀, 15–19.i.2007, 4♀, 5– 9.ii.2007, 3♀, 26.ii–2.iii.2007, S. Lanati, malaise trap ( LACM); SANTA FE: Ocampo, 28.506º S, 59.262º W, 1♀, 6.xii.2003, E.G. LeBrun, over S. invicta nest ( LACM); Romang, 29.512º S, 59.744º W, 2♀, 6.ii.2009, E.G. LeBrun, over S. invicta nest ( UTIC); BRAZIL: MATO GROSSO: Caceres Field Station, 16.5º S, 57.0º W, 1♀, 18.iv.1989, D. Williams, attacking Solenopsis ( LACM); SÃO PAULO: Campinas, near Santa Genebra Reserve, 2♀, 22.821º S, 47.105º W, xi.1995, L.E. Gilbert, attacking along Solenopsis invicta foraging trail ( LACM).

Remarks. P. obtusitus has been collected over S. invicta but has not been encountered with S. richteri , the type-host of P. obtusus . P. obtusitus may occur at both disturbed ant nests and along foraging trails ( Orr et al. 1997, Seike 2002, Folgarait et al. 2007b, Feener et al. 2008). One study ( Orr et al. 1997) found P. obtusitus more abundant on foraging trails (13/ 21 P. obtusitus/total flies) than at disturbed mounds (5/ 46 P. obtusitus/total flies).

Borgmeier (1925) described P. obtusus from material collected by Bruch at La Plata, Argentina on S. richteri . Borgmeier’s measurements make clear that P. obtusus is a large species and we found that the oviscape width of P. obtusus was consistently 0.25 to 0.31 mm, while the smaller bodied P. obtusitus has a small oviscape, not overlapping in size with P. obtusus . In earlier laboratory trials of cross mating between large P. obtusus and the smaller P. obtusitus , it appeared that mating failed since females did not go on to oviposit in host workers (P.J.F. unpublished). None of the cultures of P. obtusus reared in the United States have resulted in emergence of P. obtusitus (S.D. Porter pers. comment). Strong evidence of specific differences comes from the DNA molecular analysis of Kronforst et al. (2007), which shows a clear separation of their “small obtusus ” ( P. obtusitus ) from the larger haplotypes of P. obtusus . The variable shapes and pubescence of the flagellomere 1 and lengths of aristae of the “ obtusus ” group need further taxonomic investigation, as do the two pattern forms of P. obtusus reported by Porter & Calcaterra (2013). It is important to emphasize that in advance of P. obtusitus being designated a formal Latin binomial name this species has long been treated as a separate species in biocontrol specificity tests and introductions based on size and molecular distinctiveness ( Porter & Gilbert 2004, Plowes et al. 2011, Porter & Calcaterra 2013).

Figures

FIGURES 5 – 6. Oviscapes, dorsal-ventral view: (5) Pseudacteon obtusitus new species. Holotype. (6) Pseudacteon obtusus Borgmeier. Laboratory reared specimen, Brackenridge Field Laboratory, Austin, 068 - 01, source population Herradura, Argentina, via USDA-ARS. Scale bar 0.1 mm.